Dynamic alarm sensitivity adjustment and auto-calibrating smoke detection for reduced resource microprocessors

Abstract

A hazardous condition detection system with a sensor package employing a reduced resource microprocessor capable of dynamic alarm sensitivity adjustment having volatile and non-volatile memory which receives periodic raw sensor readings from the sensor package and preprocesses each received periodic raw sensor reading by employing at least three distinctive filtering constants which are compared to alarm thresholds stored in memory to generate an alarm condition signal when ionization levels in the ambient environment exceed stored thresholds.

1. A hazardous condition detection system, comprising,
 a housing containing a sensor package, the sensor package containing a hazardous condition sensor, the hazardous condition sensor being exposed to the ambient environment and taking periodic readings of the ambient environment; 
 an alarm circuit coupled to the sensor package and disposed in the housing; 
 a microprocessor coupled to the alarm circuit, the microprocessor having a memory storage device containing a clean air reading and a plurality of alarm thresholds differential values, each of the plurality of alarm thresholds differential values being associated with a predetermined set of sensor readings indicative of a hazardous condition in the ambient environment, 
 where said microprocessor periodically receives a raw sensor reading from the sensor package and preprocesses said received raw sensor reading using at least three distinctive filtering constants to generate a set of at least three conditioned sensor readings from each raw sensor reading received and where said microprocessor accumulates a plurality of sets of conditioned sensor readings, and selects an alarm threshold differential value from a plurality of stored alarm thresholds differential values based on the rate of change of the conditioned sensor readings in a first subset of accumulated conditioned sensor readings generated from a common filtering constant, and generates an alarm threshold from the selected alarm threshold differential value. 
 
     
     
       2. The hazardous detection system of  claim 1  characterized in that the microprocessor preprocesses each periodic sensor reading received from the sensor package according to the relation:
     V   xot =1/ N   x   *Σ[N   x   *V   o +( V   it   −V   xot-1 )] from  t   n  to  t,    
 where V xot  is the new conditioned sensor reading, N x  s a filtering constant, V o  is the clean air reading, V it  is the new raw sensor reading taken at time t, and V xot-1  is the previously generated conditioned signal at time t- 1 . 
 
     
     
       3. The hazardous condition detection system of  claim 2  characterized in that the hazardous condition sensor contained in the sensor package is a single ionization sensor. 
     
     
       4. The hazardous condition detection system of  claim 3  characterized in that the sensor package contains includes a single ionization sensor with an ion chamber that is electrically coupled to (powered by) an output pin of the microprocessor coupled to the alarm circuit. 
     
     
       5. The hazardous condition detection system of  claim 2  characterized in that the microprocessor preprocesses each periodic raw sensor reading received from the sensor package generating at least a set of V 1NEW , V 2NEW , and V 3NEW  conditioned sensor readings for each raw sensor reading received by the microprocessor from the sensor package by employing a N 1  constant of 2 14 , a N 2  constant of 2 7 , and a N 3  constant of 2 2 . 
     
     
       6. The hazardous condition detection system of  claim 5  characterized in that the first subset of accumulated conditioned sensor readings is selected from the V 2NEW  conditioned sensor readings in the accumulated sets of conditioned sensor readings generated from the raw sensor readings (t from to t- n ). 
     
     
       7. The hazardous detection system of  claim 2  characterized in that the microprocessor adjusts the value of the clean air reading to compensate for changes in the ambient conditions values based on the rate of change of the conditioned sensor readings in a second subset of accumulated conditioned sensor readings generated from a common filtering constant. 
     
     
       8. The hazardous detection system of  claim 5  characterized in that the microprocessor generates a compensated alarm threshold by adjusting the value of the clean air reading based on the rate of change of the conditioned sensor readings in a second subset of accumulated conditioned sensor readings selected from the V 1NEW  conditioned sensor readings contained in the accumulated sets of conditioned sensor readings generated from t to t- n . 
     
     
       9. The hazardous detection system of  claim 5  characterized in that the microprocessor compares the generated alarm threshold with the V 3PREV  conditioned sensor reading and designates an alarm event if the V 3NEW  conditioned sensor reading violates the generated alarm threshold. 
     
     
       10. The hazardous detection system of  claim 8  characterized in that the microprocessor compares the generated compensated alarm threshold with the V 3  conditioned sensor reading and designates an alarm event if the V 3  conditioned sensor reading violates the generated compensated alarm threshold. 
     
     
       11. A method for selecting an alarm threshold for a hazardous condition detector characterized by the method steps of:
 associating a first alarm threshold differential value with a first predetermined set of ionization levels, and a second alarm threshold differential value with a second predetermined set of ionization levels; 
 generating a first alarm threshold value from the first alarm threshold differential value; 
 designating the first generated alarm threshold value as the current alarm threshold; 
 receiving periodic raw sensor readings of the ionization level in the ambient environment from a sensor package; 
 preprocessing each received periodic raw sensor reading and generating a set of conditioned sensor readings for each received periodic raw sensor reading; 
 accumulating a plurality of sets of conditioned sensor readings; 
 generating a first subset of conditioned sensor readings by selecting a first conditioned sensor reading from each of a plurality of accumulated sets of conditioned sensor readings; 
 generating a second subset of conditioned sensor readings by selecting a second conditioned sensor reading from each of a plurality of accumulated sets of conditioned sensor readings; 
 comparing the second subset of the conditioned sensor readings with the second predetermined set of ionization levels associated with the second alarm threshold differential value with a microprocessor; 
 if the second subset of conditioned sensor readings are within the ionization levels specified in the second predetermined set of ionization levels,
 selecting the second alarm threshold differential value, 
 generating a second alarm threshold value from the selected second alarm threshold differential value, and 
 designating the second alarm threshold value as the current alarm threshold; 
 
 comparing the current alarm threshold with a third conditioned sensor selected from the newest set of conditioned sensor readings; and 
 designating an alarm event if the third conditioned sensor reading is in violation of the current alarm threshold. 
 
     
     
       12. The method according to  claim 11  further characterized by the step of:
 designating the first alarm threshold value as the current alarm threshold if the newest conditioned sensor readings from the second subset of conditioned sensor readings is less than the current alarm threshold value but greater than or equal to the preceding conditioned sensor reading in the second subset. 
 
     
     
       13. The method according to  claim 12  further characterized by the steps of:
 associating a third alarm threshold differential value with a third predetermined set of ionization levels; 
 comparing the second subset of the conditioned sensor readings with the third predetermined set of ionization levels associated with the third alarm threshold differential value with a microprocessor;
 if the conditioned sensor readings in the second subset are within the ionization levels specified in the third predetermined set of ionization levels associated with the third alarm threshold, 
 selecting the third alarm threshold differential value, 
 generating a third alarm threshold value from the selected third alarm threshold differential value, and 
 designating the third alarm threshold value as the current alarm threshold. 
 
 
     
     
       14. The method according to  claim 12  further characterized by the step of:
 preprocessing each periodic sensor reading received from the sensor package according to the relation:
     V   xot =1/ N   x   *Σ[N   x   *V   o +( V   it   −V   xot-1 )] from  t   -n  to  t,    
 
 where V xot  is the new conditioned sensor reading, N x  is a filtering constant, V o  is the clean air reading, V it  is the new raw sensor reading taken at time t, and V xot-1  is the previously generated conditioned signal at time t- 1 . 
 
     
     
       15. The method according to  claim 14  characterized by the step of preprocessing each periodic raw sensor reading received from the sensor package generating at least a set of V 1NEW , V 2NEW , and V 3NEW  conditioned sensor readings for each raw sensor reading received by the microprocessor from the sensor package by employing a N 1  constant of 2 14 , a N 2  constant of 2 7 , and a N 3  constant of 2 2 . 
     
     
       16. The method according to  claim 15  characterized by the step of selecting the first subset of accumulated conditioned sensor readings from the V 2  conditioned sensor readings in the accumulated sets of conditioned sensor readings generated from the raw sensor readings (from t n  to t). 
     
     
       17. The method according to  claim 14  characterized by the step of adjusting the generated alarm threshold to compensate for changes in the ambient conditions values based on the rate of change of the conditioned sensor readings in a second subset of accumulated conditioned sensor readings generated from a common filtering constant. 
     
     
       18. The method according to  claim 15  characterized by the step of generating a compensated alarm threshold by using a microprocessor to adjust the value of the generated alarm threshold based on the rate of change of the conditioned sensor readings in a second subset of accumulated conditioned sensor readings selected from the V 1NEW  conditioned sensor readings in the accumulated sets of conditioned sensor readings generated from the raw sensor readings (from t n  to t) and comparing the V 3NEW  conditioned sensor reading with the V 3PREV  and designating an alarm event if the generated alarm threshold has been violated. 
     
     
       19. The method according to  claim 11  further characterized by the step of:
 conditioning each ionization reading received by removing a selected amount of noise and attenuation therefrom. 
 
     
     
       20. The method according to  claim 19  further characterized by the step of:
 conditioning each raw sensor reading received by removing a selected amount of noise and attenuation therefrom, and generating a conditioned sensor reading according to the relation:
     V   xot =1/ N   x   *Σ[N   x   *V   o +( V   it   −V   xot-1 )] from  t   -n  to  t,    
 
 where V xot  is the new conditioned sensor reading, N x  is a filtering constant, V o  is the clean air reading, V it  is the new raw sensor reading taken at time t, and V xot-1  is the previously generated conditioned signal at time t- 1  and each of said plurality of filtering constants is selected by the microprocessor to generate a set of conditioned readings each having a signal to noise ratio optimized for a particular processing step.